Surface plasma wave coupled detectors

ABSTRACT

The present disclosure relates to an electromagnetic energy detector. The detector can include a substrate having a first refractive index; a metal layer; an absorber layer having a second refractive index and disposed between the substrate and the metal layer; a coupling structure to convert incident radiation to a surface plasma wave; additional conducting layers to provide for electrical contact to the electromagnetic energy detector, each conducting layer characterized by a conductivity and a refractive index; and a surface plasma wave (“SPW”) mode-confining layer having a third refractive index that is higher than the second refractive index disposed between the substrate and the metal layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.14/213,691 filed Mar. 14, 2014 (now allowed), which claims benefit toU.S. Provisional Patent Application Ser. No. 61/787,570, titled“Optimization of Surface Plasma Wave Coupled Detectors,” filed on Mar.15, 2013, and is related to U.S. patent application Ser. No. 13/502,987(now U.S. Pat. No. 8,835,851), which claims priority to U.S. ProvisionalPatent Application Ser. Nos. 61/279,435, filed on Oct. 21, 2009 and61/339,185, filed on Mar. 1, 2010, which are hereby incorporated byreference in their entirety.

GOVERNMENT INTEREST

This invention was made with U.S. Government support under Grant No.FA9550-12-1-0049 awarded by the Air Force Office of Scientific Research.The U.S. Government has certain rights in the invention.

TECHNICAL FIELD

This disclosure generally relates to plasmonic detectors. In particular,this disclosure relates to plasmonic structures and their use inresonantly enhancing the performance of infrared detectors.

BACKGROUND

There is increasing interest in using surface plasma waves or otherbound local modes to both increase the interaction of incident radiationwith detectors and also to provide spectral selectivity. Ongoing workcovers both the infrared and the visible spectral regions.

In the visible there is a need for spectral/angular resolutioncompatible with inexpensive silicon fabrication. While color cameras areubiquitous, the spectral resolution is provided typically by absorbingdyes, which are increasingly difficult to fabricate with sufficientabsorbance as the pixel size decreases, and provide only limitedspectral selectivity.

In the infrared, detector signal-to-noise is an important driver.Detectors cooled to cryogenic temperatures provide the highestsensitivity, but require extensive and expensive infrastructure limitingtheir applicability. Uncooled detectors, typically based on thermalheating of an isolated structure by infrared radiation, have limitationsassociated with high noise levels and limited response speed.

Surface plasma wave (SPW) and other guided mode interactions provide amethod to address some of these issues. There are two related classes ofSPWs. For a planar interface between a metal and a device layer (such asa semiconductor material), there is a mode bound to the interface (e.g.,a slow wave that is propagating along the interface and evanescent(exponentially decreasing in amplitude) into both the metal and thedevice layer). This wave is well defined for Re(−Σ_(m))>Re(Σ_(d)) whereΣ_(m) is the permittivity of the metal (with a negative real part) andΣ_(d) is the dielectric permittivity. For isolated metal structures,there are localized SPW resonances that concentrate the fields, thislocalized resonance is involved in the well-known surface enhanced Ramanscattering (SERS) effect.

Much of the analysis of SPW modes at a planar metal/dielectric interfacehas considered only a simple two component structure with a top metal,most often the metal layer incorporates a 1D or 2D grating structure toprovide the necessary coupling to the slow SPW and a semi-infinitedielectric layer (e.g., to allow for momentum conservation). However, arealistic detector structure has multiple device layers with varyingpermittivities. These layers could include contact layers with p- andn-type doping, absorber layers (e.g., quantum dots or strained layersuperlattices in the infrared), and electrical isolation layers (oftenof much lower permittivity than the semiconductor). These layers canhave a profound effect on the coupling to, and even to the existence of,the SPW and need to be considered in a full device analysis and design.Additionally, this simple two material model typically does not allowfor separate indentification of the useful absorption in the absorberlayer and of the parasitic absorption in the metal layer and are hencenot sufficient for detailed designs.

INCORPORATION BY REFERENCE

The following references are incorporated by reference in theirentirety:

-   S. C. Lee, S. Krishna, and S. R. J. Brueck, “Light    direction-dependent plasmonic enhancement in quantum dot infrared    photodetectors,” Applied Physics Letters 97, 02112 (2010).-   S. C. Lee, Y. D. Sharma, S. Krishna, and S. R. J. Brueck,    “Leaky-mode effects in plasmonic-coupled quantum dot infrared    photodetectors,” Applied Physics Letters 100, 011110 (2012).-   S. C. Lee, S. Krishna, and S. R. J. Brueck, “Quantum dot infrared    photodetector enhanced by surface plasma wave excitation,” Optical    Society of America, Optics Express, Vol. 17, No., Dec. 7, 2009.-   S. J. Lee, Z. Ku, A. Barve, J. Montoya, W. Y. Jang, S. R. J.    Brueck, M. Sundaram, A. Reisinger, S. Krishna, and S. K. Noh, “A    monolithically integrated plasmonic infrared quantum dot camera,”    Nature Communications, DOI: 10.1038/ncomms1283.-   Z. Ku, W. Y. Jang, J. Zhou, J. O. Kim, A. V. Barve, S. Silva, S.    Krishna, S. R. J. Brueck, R. Nelson, A. Urbas, S. Kang, and S. J.    Lee, “Analysis of subwavelength metal hole array structure for the    enhancement of black-illuminated quantum dot infrared    photodetectors,” Optical Society of America, Optics Express, Vol.    21, No. 4, Feb. 25, 2013.-   J. Chen, G. A. Smolyakov, S. R. J. Brueck, and K. J. Malloy,    “Surface plasmon modes of finite, planar, metal-insulator-metal    plasmonic waveguides,” Optical Society of America, Optics Express,    Vol. 16, No. 19, Sep. 15, 2008.

SUMMARY

In accordance with implementations consistent with the presentteachings, an electromagnetic energy detector is disclosed. The detectorcan comprise a substrate having a first refractive index; a metal layer;an absorber layer having a second refractive index and disposed betweenthe substrate and the metal layer; a coupling structure to convertincident radiation to a surface plasma wave; additional conductinglayers to provide for electrical contact to the electromagnetic energydetector, each conducting layer characterized by a conductivity and arefractive index; a surface plasma wave (“SPW”) mode-confining layerhaving a third refractive index that is higher than the secondrefractive index disposed between the substrate and the metal layer.

In implementations, the SPW mode-confining layer can be disposed betweenthe substrate and the absorber layer. Alternatively, the SPWmode-confining layer can be disposed between the absorber layer and themetal layer.

In implementations, the detector can comprise a top contact layer havinga fourth refractive index that is lower than the second refractive indexand disposed between the substrate and the metal layer.

In implementations, the detector can comprise a top contact layer havinga fourth refractive index that is higher than the second refractiveindex and disposed between the substrate and the metal layer.

In implementations, the detector can comprise a bottom contact layerhaving a fifth refractive index that is lower than the second refractiveindex and the fourth refractive index and disposed between the substrateand the metal layer.

In implementations, the detector can comprise a bottom contact layerhaving a fifth refractive index that is higher than the secondrefractive index and the fourth refractive index and disposed betweenthe substrate and the metal layer.

In implementations, the absorber layer can comprise a strained layersuperlattice (“SLS”). In implementations, the SLS can comprise InAs:GaSbhaving a thickness ˜0.09 μm.

In implementations, the absorber layer can comprise a plurality ofquantum dots designed for absorption at the detector operatingwavelength.

In implementations, the metal layer can comprise Au, Ag, or Al.

In implementations, the coupling structure can comprise an array ofholes in the metal film.

In implementations, the coupling structure can comprise a semiconductorlayer with post structures etched or deposited therein and the metallayer comprises a continuous metal layer.

In implementations, the coupling structure can be patterned and themetal layer can comprise a corrugated metal layer.

In implementations, the detector can further comprise at least one dopedcontact layer.

In implementations, the detector can further comprise at least oneetch-stop layer.

In implementations, the SPW mode-confining layer can comprise Ge.

In implementations, the substrate can comprise GaSb.

In implementations consistent with the present teachings, a method offorming an electromagnetic energy detector is disclosed. The method cancomprise forming a metal layer on a substrate, the substrate having afirst refractive index; forming an absorber layer having a secondrefractive index between the substrate and the metal layer; forming acoupling structure in the vicinity of the metal layer to couple incidentradiation into surface plasma waves confined to and propagating alongthe metal device layer interface; and forming a surface plasma wave(“SPW”) mode-confining layer having a third refractive index that ishigher than the second refractive index between the substrate and themetal layer.

In implementations, the SPW mode-confining layer can be formed betweenthe substrate and the absorber layer.

In implementations, the SPW mode-confining layer can be formed betweenthe absorber layer and the metal layer.

In implementations, the coupling structure is formed within theevanescent length of the decay in the device layer and the metal layerto couple incident radiation into surface plasma waves confined to, andpropagating along the metal dielectric interface.

In implementations, a method of detecting electromagnetic radiationusing the device is disclosed.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the application, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the applicationand together with the description, serve to explain the principles ofthe application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simplified schematic of a layered detectorstructure according to some embodiments.

FIG. 2 shows a plot of a modal calculation for the Au surface plasmawave bound to a SLS/GaSb structure at a wavelength of 4 μm according tosome embodiments.

FIG. 3 shows a plot of real and imaginary parts of the modal index withthe thickness of a Ge overlayer as a parameter according to someembodiments.

FIG. 4 shows a plot of modal loss for t_(Ge)=0.5 mm, where the overallloss is decreased since the absorber layer is moved deeper into thematerial where the fields have decay somewhat, according to someembodiments.

FIG. 5 shows a plot of a Figure of Merit (FOM) for an SLS SPW detectoraccording to some embodiments.

FIG. 6 shows another detector structure according to some embodiments.

FIG. 7 shows another detector structure according to some embodiments.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the principles of the presentteachings are described by referring mainly to exemplary embodimentsthereof. However, one of ordinary skill in the art would readilyrecognize that the same principles are equally applicable to, and can beimplemented in, all types of information and systems, and that any suchvariations do not depart from the true spirit and scope of the presentteachings. Moreover, in the following detailed description, referencesare made to the accompanying figures, which illustrate specificexemplary embodiments. Electrical, mechanical, logical and structuralchanges may be made to the exemplary embodiments without departing fromthe spirit and scope of the present teachings. The following detaileddescription is, therefore, not to be taken in a limiting sense and thescope of the present teachings is defined by the appended claims andtheir equivalents.

Reference will now be made in detail to the exemplary embodiments.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

FIG. 1 illustrates an example simplified schematic of a layered detectorstructure 100 in accordance with implementations consistent with thepresent teachings. While FIG. 1 illustrates various features of anexample simplified schematic of a layered detector structure 100, oneskilled in the art will realize that the illustrated detector structureis exemplary and that the detector structure 100 can include additionalcomponents and layers, such as heavily-doped contact layers andetch-stop layers that are used for separation of the device layers fromthe substrate.

As illustrated in FIG. 1, the layered detector structure 100 comprises asubstrate 105 composed of, e.g., GaSb ((Σ_(d)=14.45=(3.801)²), GaAs, andother bulk III-V materials, HgCdTe, an absorber layer 110, e.g., astrained layer superlattice (“SLS”) absorber layer composed of materialsincluding, but are not limited to, a lower permittivity InAs:GaSb SLSabsorber layer (12.25 (InAs)<Σ_(d)<14.45 (GaSb) depending on therelative composition; thickness t), a plurality of quantum dots composedof InAs or InGaAs, a plurality of quantum wells composed of InGaAs andAlInGaAs, a plurality of quantum dots-in-a-well (DWELL), InAs dots in anInGaAs well, a cladding layer 115 composed of e.g., Ge with a thicknessto be discussed below, GaAs, GaSb, InAs, and a metal layer 120 composedof e.g., Au, Ag (which is a better metal (lower loss) in the visible),Al is metallic to shorter wavelengths than either Au or Ag. Othermaterials useful for infrared photodetectors that can be used includemercury cadmium telluride (HgCdTe) and indium antimonide (InSb).

The structure 100 of FIG. 1 can be illustrative of some of the issuesencountered with theses type of devices. Often the materials of theabsorber layer 110, the cladding layer 115, and the metal layer 120 havea different index of refraction than the materials of the substrate 105.If there is layer within the structure 100 composed of a material havinga lower index of refraction than the substrate material, then thestructure 100 can exhibit leaky mode behavior, which can result in adecrease of the coupling of light into the substrate 105 and, thus, adecrease in sensitivity of a detector comprising the structure 100. FIG.2 shows a plot of the calculated modal behavior (real and imaginaryparts) as a function of the thickness of the absorber layer 110 for avery simple structure with only a metal film (Au) for the metal layer120, a SLS absorber layer 110 of variable thickness and a GaSb substrate105 (e.g., no cladding layer). The calculation is for a wavelength of 4μm, in the mid-wave infrared. A conventional transfer matrix analysiswas used for this calculation as is known in the art.

As shown in FIG. 2, the loss [Im (modal index)] without any SLSthickness is the background loss associated with the metal opticalproperties. This is equivalent to the loss shown for a 1 nm thick SLSlayer on the left hand side of FIG. 2. The excess loss as the SLSthickness is increased is the “useful” absorption that leads toelectrical response of the detector. At an SLS thickness of severaltenths of a μm, this loss plummets. This is the onset of the leaky moderegime as the real part of the modal index passes through the substrateindex. Around this point, the mode extends deep into the substrate andthere is very little of the mode intensity at the absorber and thereforea dramatic reduction in the useful absorption. This is the onset of theleaky mode regime.

This issue can be resolved by adding the cladding layer 115 composed ofa material having an index of refraction that is at least as high asthat of the material of the substrate 105. The addition of the higherindex of refraction cladding layer 115 does come with a necessarycompromise. If the cladding layer 115 is too thin, the modes of incidentradiation are not effectively bound to the vicinity of the absorberlayer 110. If the cladding layer 115 is too thick, the absorber layer110 becomes too distant from the strong fields of the incident radiationand results in a decrease in the absorption. These effects areillustrated in FIG. 3 which shows the modal indices (top real part,bottom imaginary part) with the thickness of a high-index Ge layer(n_(Ge)˜4.0) as a parameter.

The results demonstrate that the SPW or other bound mode is bound to thesurface of the absorber layer 110, which allows an increase in thicknessof the absorber layer 110 or other layers underneath the cladding layer115. The curve for t_(Ge)=0 was also shown in FIG. 2 and is repeatedhere. As the thickness of the cladding layer 115, composed in thisexample of Ge, is increased, the mode becomes increasingly bound to thesurface of the absorber layer 110 and the leaky mode regime is avoided.For t_(Ge)=0.05 μm there is still a significant dip in the absorptionthat recovers as the thickness of the SLS is increased. This dip isstill barely apparent for t_(Ge)=0.1 μm, and is entirely eliminated fort_(Ge)=0.2 μm.

For still thicker Ge cladding layer 115, the absorber layer 110 is movedfurther into the sample, and the absorption decreases as a result of theevanescent decay of the mode into the sample. This is shown in FIG. 4which shows the imaginary part for thicker Ge layers of 0.2- and 0.5-μm.

The above-discussed considerations can combined all of this into afigure of merit for the detector. For a conventional double passgeometry (illuminate through the substrate and reflection from a metalfilm on top of the epitaxy), the figure of merit is:

${FOM} = \frac{\left( {1 - e^{{- 8}\pi\;{{kT}_{SLS}/\lambda}}} \right)}{\sqrt{T_{SLS}}}$where K is the imaginary part of the refractive index of the absorber atwavelength λ and T_(SLS) is the thickness of the SLS absorber layer. Thefactor of 1/√{square root over (T_(SLS))} accounts for the detector GRnoise, proportional to the square root of the active volume. The factorof 8 is due to 2*2*2π where the first 2 is from the double pass, thesecond 2 is the result of considering power rather than field strength,and the 2π is just part of the wavevector k₀=2π/λ. For the SPW enhanceddetector, the equivalent expression is:

${FOM} = \frac{\left( {1 - e^{{- {KT}_{SLS}}4{\pi/\lambda}}} \right) + {e^{{- {KT}_{SLS}}4{\pi/\lambda}}\frac{K - K_{m}}{K}\left( {1 - e^{{- 4}\;\pi\;{{KP}/\lambda}}} \right)}}{\sqrt{T_{SLS}}}$where the first term in the numerator accounts for the absorption on thefirst pass through the absorber layer 110 from the substrate side. Theenergy transmitted through the absorber layer 110 is then coupled to theSPW mode, the term (K-K_(m))/K accounts for the loss into the metal thatdoes not provide useful signal (assuming 100% for the couplingefficiency of the radiation that passes through the absorber into thesurface plasma wave at the metal:semiconductor interface). The followingexponential accounts for any energy that is not absorbed within thewidth of the pixel P (=25 μm). The value for K_(m) is obtained byevaluating the loss of a comparable structure without any absorption inthe SLS, but with the same real part of the dielectric constant to mimicthe field distribution.

FIG. 5 shows a plot of the FOM for an SLS SPW detector. The comparisonis to a traditional double pass configuration. In the shaded regionmarked “Leaky Mode Regime,” the values for the lossless configurationare not reliable (since some of the calculated loss is actuallyradiation loss). The Ge cladding layer 115 stabilizes the lossy (e.g.,with SLS absorption) so that everything is well defined but there is noway to calculate the fraction of the energy absorbed in the SLS. Sincethis regime is not at the peak FOM, this does not impact the conclusionsor design point. This calculation is for a simple structure withoutcontact layers. These are simple to add and do not impact theconclusions.

Three points are specifically callout out (arrows) on FIG. 5. For atraditional double pass geometry the highest FOM of 0.36 is found at aSLS thickness of ˜3- to 4-μm. For thinner layers there is insufficientabsorption and for thicker layers the noise increases without additionalabsorption. In contrast, the optimal FOM for the SPW detectors is at anSLS thickness of ˜0.09 μm (this does depend on the pixel width, 25 μmfor this calculation). The peak FOM is about 1.5, an improvement of420%. At the same SLS thickness, the double pass detector shows a FOM ofonly 0.03, a factor of 50 lower than the SPW case. This figure is at thedesign wavelength of the detector (which was taken as 4 μm for thecalculation). The design wavelength can be shifted by changing the pitchof the coupling structure.

As noted above, a periodic variation is needed to provide for couplingfrom free space radiation to the surface plasma wave. In someimplementations, the metal layer, e.g., metal film 120 can be modifiedto include a metal photonic crystal (MPC), which is a metal filmperforated with an array of holes, as shown in FIG. 6. The MPC can besubstituted in place of metal layer 120 or formed on top of metal layer120. Additionally or alternatively, the MPC can be formed at the bottomof the structure and adjacent to the substrate 105. The MPC can enhancethe coupling of the incident radiation to the structure, allowing theabsorber layer 110 to receive a larger portion of the incidentradiation. Contact layers 150 are formed on either side of absorberlayer 110 providing an interface 102 between a contact layer of contactlayers 150 and absorber layer 110. Additionally or alternatively, thestructure 100 can be modified by coupling the bottom surface of thesubstrate 105 with a corrugated metal surface (CMS), which is an arrayof posts etched into the semiconductor covered with a continuous Aufilm, as shown in FIG. 7. The CMS design completely decouples theoptical properties from any materials, such as In-solder bumps, that areadded on top of the Au film for integration with a read-out integratedcircuit (ROIC). This makes the design fully compatible with existingindustry manufacturing practices. The performance of the detector can beoptimized for different applications (e.g., broad band vs. narrow band,coupling wavelength and coupling strength) by changing the properties ofthe coupling structure.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as is apparent.Functionally equivalent methods and apparatuses within the scope of thedisclosure, in addition to those enumerated herein, will be apparentfrom the described descriptions. Such modifications and variations areintended to fall within the scope of the appended claims. The presentdisclosure is to be limited only by the terms of the appended claims,along with the full scope of equivalents to which such claims areentitled. It is to be understood that this disclosure is not limited toparticular methods, which can, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, suchrecitation should be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, means at least two recitations, or two or more recitations).Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). In those instances where a conventionanalogous to “at least one of A, B, or C, etc.” is used, in general sucha construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, or C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

Other embodiments of the disclosure will be apparent to those skilled inthe art from consideration of the specification and practice of theembodiments disclosed herein. In particular, it should be appreciatedthat the processes defined herein are merely exemplary, and that thesteps of the processes need not necessarily be performed in the orderpresented. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theembodiments being indicated by the following claims.

What is claimed is:
 1. A method of forming an infrared (IR)electromagnetic energy detector, comprising: forming a metal layer on asubstrate, the substrate having a first refractive index; forming anabsorber layer having a second refractive index between the substrateand the metal layer; forming a coupling structure in the vicinity of themetal layer to couple incident radiation into surface plasma wavespropagating along an interface between the metal layer and the absorberlayer; and forming a surface plasma wave (“SPW”) mode-confining layerbetween the metal layer and the substrate having a third refractiveindex that is higher than the second refractive index at IR wavelengths.2. The method of claim 1, wherein the SPW mode-confining layer is formedbetween the substrate and the absorber layer.
 3. The method of claim 1,wherein the coupling structure is formed within an evanescent length ofa decay in the absorber layer and the metal layer to couple incidentradiation into surface plasma waves propagating along the interface. 4.The method of claim 1, further comprising forming a top contact layerhaving a fourth refractive index that is lower than the secondrefractive index.
 5. The method of claim 4, further comprising forming abottom contact layer having a fifth refractive index that is lower thanthe second refractive index and the fourth refractive index and disposedbetween the substrate and the absorber layer.
 6. The method of claim 1,wherein the absorber layer comprises a strained layer super lattice(“SLS”).
 7. The method of claim 6, wherein the SLS comprises InAs:GaSbhaving a thickness—0.091-1 m.
 8. The method of claim 1, wherein theabsorber layer comprises a plurality of quantum dots.
 9. The method ofclaim 1, wherein the metal layer comprises Au or Ag.
 10. The methodclaim 1, wherein the coupling structure comprises a hole array.
 11. Themethod of claim 1, wherein the coupling structure comprises asemiconductor layer with post structures etched or deposited therein andthe metal layer comprises a continuous metal layer.
 12. The method ofclaim 1, wherein the coupling structure is patterned and the metal layercomprises a corrugated metal layer.
 13. The method of claim 1, whereinthe SPW mode-confining layer comprises Ge.
 14. The method of claim 1,wherein the substrate comprises GaSb.